US2091905A - Electric resistance heating element - Google Patents

Description

Aug. 31,1937.

A. BENS'E'L :r AL ELECTRIC RESTSTANCE HEATING ELEMENT Filed Sept. 9, 1935 2 Sheets-Sheet 1 v M A-Benael and W Aprau Aug. 31, 1937. A. BENSEL ET AL I ELECTRIC RESISTANCE HEATING ELEMENT Filed se t. 9, 1935 2 Sheets-Sheet 2 I 4 I r I 5 I I A 361188] and Brawn Patented Aug. 31, 1937 ELECTRIC RESISTANCE HEATING ELEMENT Arlington Bensel. East Orange, .N. 1., and William A. Braun, Dover, Ohio Application September 9, 1935, Serial No. 39,676

10 Claims. (01. 219,-)

The invention relates to electric resistance heating elemets for use more particularly in elecric stoves for cooking purposes. Such elements in general utilize relatively high resistance re- 'sistors made of material such as a nickel chrome alloy which becomes ultimately red hot upon the passage therethroush of an electric current of suitable voltage and amperage, the resistors be.-

ing suitably insulated and supported on frames or bases of the elements.

The most economical way to produce resistors for use in electric resistance heating elements for cooking stoves has been found to make helical coils of high resistance wire, one or more of which v positioned, so as to provide spaced turns or lengths oi the coils relatively close to each other in order to provide the necessary concentration of heat in the cooking area of the element.

When the coils of elements are upwardly exposed, as in many usualelectric cooking stoves, there is danger of short circuiting and burning out of the elements by accidental contact with the coils of utensils, such as forks, or by spilling solid food particles or liquids on the coils.

To overcome such dangers, the coils of certain elements for electric stoves have been entirely sheathed by embedding the coils in insulating material such as highly refractory cement of the nature of aluminum oxide, and sometimes by embedding the coils in magnesium oxide and enclosing such embedded coils in metallic tubes of steel or alloy steel, the tubes being sealed under pressure, thus subjecting the enclosed insulating material and resistors to pressure.

In other instances upper and lower sheath plates joining at their peripheries are used teenclose resistors embedded in insulating material.

Entirely sheathed coils are relatively high in cost and diflicult to manufacture, and very fre-' quently break down in use; that is, the insulating material is altered in its characteristics 45 through contamination or influence'of gas and vapor emitted from the coils, sheath, or both, at certain temperatures, causing the insulating material to lose its di-electric strength, and to lower its voltage breakdown point.

In extreme cases a metallic film has been formed on the insulating material and between the turns of the coils as a result of such chemical reaction or gassing and vaporizing of the enclosed members. 55 From the physical standpoint, in elements havcoils are arranged in a spiral, or in concentric rings, or paralleled back and forth, or otherwise ing resistor coils embedded in insulating material and entirely sheathed by metallic tubes or shells, the sheath, insulating material, and coils, each have a different co-eilicient of thermal expansion, and there is set up in the element opposing strains 5 in theseveral parts due to heating and cooling of the element in use, which strains frequently result in damage to the insulating material or coils requiring a replacement of the element.

From another standpoint the heat generated 10 in a radiant electric resistance coil may be transmitted to a cooking utensil placed upon the element of which the coil is a part by the four different methods of heat transmission: namely, conduction, convection, radiation, and reflection. 15 In usual electric resistance heating elements having sheathed coils, oneor more of four modes of heat transmission are not utilized, r are utilized only to a limited degree, particularly convection, radiation, and reflection, with a consequent loss of a portion of the total heat generated.

From still another standpoint, electric resistance heating elements having sheathed coils do not give any visible evidence of the heat therein until some considerable period of time has elapsed after the switch of the element has been turned to pass current through the coils, so that the operator does not have any quick evidence that the element is functioning and heat is being emitted. 0 There is also danger of burns when the operator has forgotten that the current has been turned into the element and accidentally touches the hot element, or when more than one person is using the stove and one or moreelements thereof may be turned on by one operator without the knowledge of one or more ofithe other operators, who may accidentally touch one of the hot elements.

The objects of the present invention include in ge eral the provision of an improved electric resist ce heating element particularly adapted for safe and emcientjiuse in a cooking stove, having a simplified construction, and being economical to 'make.

More particular objects of the present invention include the provision of an improved electric resistance heating element in which are attained substantially all of the advantages of an element having totally sheathed resistor coils, without being subject to the disadvantages of totally sheathed coils givingrise to a breakdown .of the insulation and burning out or breaking of the coils, either as the result of the emission of gases or vapors, or expansion and contraction due to heating and cooling.

sub-combinationa' which comprise the present invention, and the nature of which is set forth in the following general statement, and preferred l embodiments of which, together with their mode of use are set forth in the following description,

and which are particularly and distinctly p'oint-,

ed out and set forth in the appended claims forming part hereof.

The nature of the improvements of the present invention may be described in general terms as including in an electric resistance heating element, a sheath plate, preferably made of either cast or pressed metal, and having spaced aper- 2 tuees formed therein, which are preferably elona ed.

In use, the upper surface of the sheath plate constitutes the cooking plane or area upon which the pan, kettle, or other utensil is placed for the 30 purpose of cooking liquids or solids contained therein.

The improved element furthermore includes on the underside of the sheath plate an elongated resistor preferably made of a helical coil of high resistance wire such as nickel chrome alloy and which is located between the apertures.

Insulating means secure the resistor to the underside of the sheath plate, the sheath plate preferably having grooves on its underside in 40 which the resistor is located and which are filled with an insulating ceramic material such as aluminum oxide which embeds and holds the upper portions of the turns of the preferably coil resistor, the lower portions of the turns of the 45 resistor being exposed downwardly.

Reflecter means are spaced from the sheath plate and from the resistor at the underside or I Fig. 2, an enlarged transverse sectional view 1 thereof as on line 2-2, Fig. 1;

Fig. 3, a view thereof looking towards the underside of the sheath plate;

65 electric resistance heating element embodying the present improvements and having a pressed metal sheath plate;

Fig. 5, a transverse sectional view thereof as on line 5-5, Fig. 4;

illustrating in detail the resistor coil of the element of Figs. 1 to 3 inclusive and the insulating material mounting the upper portions of the 75 turns of the coil in one of the grooves of the Fig. 4, a plan view similar to Fig. 1 of anothe Fig. 6, an'enlarged fragmentary sectional view Y sheath plate, the grooves having a flat bottom and flat sides; and

Fig. 7, a view similar to Fig. 6 illustrating a modified form of groove having a semi-circular cross-section. v

Similar numerals refer to similar parts throughout the several views.

One embodiment of the present improvements is illustrated in Figs. '1, 2, 3, and 6 and consists of an electric resistance heating element indicated generally by I0 and including a metal sheath plate II, which as shown is circular and hasa flat top I2 with a cylindrical flange I3 extending downwardly from the outer periphery of the plate II. 7

The plate II has formed therein a plurality of radially spaced elongated arcuate apertures I4 and a central circular aperture I5.

As shown, a cylindrical flange I6 extends downwardly from the plate II about the periphery of the central aperture I5, and also as shown there is provided a cylindrical flange I'I extending downwardly from the plate II radially spaced between the flange I3 and the flange I6.

Between the apertures I4, the plate II has formed therein on'its underside, a plurality of radially spaced elongated arcuate and downwardly opening grooves I8.

Elongated resistors I9, which as illustrated are helical coils of high resistance wire such as nickel chrome alloy, are located in the grooves I8, and the upper half portions of the turns of the coils- I9 are embedded in insulating material 20 such as aluminum oxide which serves to secure the coils in the grooves I8 and to the under-.

side of the plate II. The lower half portions of the'turns of the coils I9 are exposed and protrude from the embedding insulating material.

Reflector means indicated generally by 2| are As shown, the reflector means 2| is preferably v a one-piece member 22 having a convex conical reflecting surface 23 formed on its inner surface opposite the coils I9.

The reflector member 22 also has formed therein' a central aperture 24 and a side aperture 25. a The improved electric resistance heating element I0 as illustrated, and as best shown in Fig. 3 includes two separate resistor coils I9, one having terminals at 26 and 21, and the other having terminals at 28 and 29. V

The terminals of the separate coil's are connected in'a' usual manner bymeans not shown with conductors not shown of an electric power supply line, which'may pass through the side aperture 25 of the reflector member .22.

The coil resistors I9 as shown are arranged between the apertures I4 on the underside of the sheath plate II in side by-side circular grooves I8. I'he ends of some of the side by side grooves are connected with each other by elbows 30 so as to permit a desired continuous length of wire in each resistor coil I9.'

In the electric resistance heating element I0, the downwardly opening. grooves I8 have flat bottom faces 3| and flat side faces 32 and 33 as best shown in Fig. 6. I

The sheath plate II with the apertures I4, the flanges I3, I6, and I1, and the grooves I8, are as illustrated in the form of acne piececasting indicated by 34, and which may be of metal, such as cast iron, or vitrified ceramic material.

In Fig. 7 is illustrated a modified sheath plate Ill having a modifled groove 8 formed therein, which has atransverse, semi-circular cross-section, and side flanges retaining the insulation material.

Another embodiment of the present improvements is illustrated in Figs. 4 and 5 in the electric resistance heating element indicated generally by the turns of the coils 2|9 are secured in the grooves ofthe troughs M8 and to the sheath plate 2 by insulating material 220 which may be aluminum oxide.

The reflector means HI of the element 2"! as shown is the same as the reflector means 2| for the element l0.

The mode of operation of the improved electric resistance heating element It comprising one embodiment of the present improvements, and of the electric resistance heating element 2H] comprising another embodiment of the present improvements, is the same, and will be described for convenience by reference to the element l0.

Locating the resistor coils l9 between the apertures I I on the underside of the sheath plate ll issuch that the flat top I2 01 the sheath plate ll constituting the heating plane or area of the element l0, presents upwardly only a supporting surface for a pan or kettle, and from the standpoint of preventing any accidental striking of the coiis of the resistors IS with a utensil, such as a fork, or any pouring of food or liquids thereover, the sheath plate H with only its upper metallic surface exposed, operates in substantially the same manner as if the coils l9 were entirely sheathed.. n v

The exposure of the lower half portions of the turns of the coils of the conductors l9 serves to permit free escape of any gases or vapors which may be given of! by the wire at certain tempera-- tures, and thus does not result in any destruction thereby oi the insulating material 20, resistor coil, or both, by chemical action or by physical strains.-

From the standpoint of heat transmission in the improved electric resistance heating element l0, heat is transmitted to the heating plane i2 at the outer upper side or face of the sheath plate I II by the tour methods of heat transmission:

namely, conduction, radiation, reflection, and 0 convection.

Conduction is efiected through the plate H.

, Radiation is efiected from the coils l9 which become luminous and give of! visible light rays and also which give ofl! invisible radiant heat rays extending in all directions from the coils IS.

The invisible radiant rays directed downwardly from the coils H are reflected by the reflector means 2| up through the apertures II, and the reflector means 2| also reflect the light rays from 7 the radiant coils I! quickly through the apertures ll, thus giving quick evidence that the element is in operation.

"Theair adjacent the coils llbecomes hot, and convection through the reflector means aperture 75 2G and the apertures l4 and l5 0! the plate ll serves also to transmit heat from the coils i9 to the heating plane or area ii.

The improved electric resistance heating elements of the invention, several embodiments of which have been set forth in detail above by way of example, attain the objects of the invention as above set forth, whereby the heat from the resistors is transmitted to the heating plane or area at theouter surface of the sheath plates with a maximum efliciency, thereby resulting in a reduced cost of operation as compared with usual electric resistance heating elements.

We claim: I

1.'In electric resistance heating apparatus, a sheath plate having spaced apertures formed therein, an elongated electrical resistor adapted for having an electric current passed therethrough, insulating means securing portions of the resistor to one side of the sheath plate, the resistor being located between the apertures and having elongated exposed portions, and reflector.

therethrough, insulating means securing portions of the resistor to one side of the sheath plate, the resistor being locatedbetween the apertures and having elongated exposed portions, and reflector means spaced from the sheath plate and the resistor at the resistor side thereof, whereby heat from the resistor is transmitted to the plane of the other side of the sheath plate by conduction, convection, radiation, and reflection.

3. In electric resistance heating apparatus, a.

metal sheath plate having spaced apertures formed therein, an elongated electrical resistor adapted for having an electric current passed therethrough, insulating means securing portions of the resistor to one side of the metal sheath plate, the resistor being located between the apertures and having elongated exposed portions, and reflector means spaced from the metal sheath plate and the resistor at the resistor side thereof, whereby heat from the resistor is transmitted to the plane of the other side of the metal sheath plate by conduction, convection, radiation, and reflection. v

4. In electric resistance heating apparatus, a metal sheath plate having spaced elongated apertures formed therein, an elongated electrical resistor adapted for having an electric current passed therethrough, insulating means securing portions of the resistor. to one side of the metal sheath plate, the resistor being located between the apertures and having elongated exposed portions, and reflector means spaced from the metal sheath plate and the resistor at the resistor side thereof, whereby heat from the resistor is transmitted to the plane of the other side ofthe metal sheath plate by conduction, convection, radiation, and reflection.

'5. In electric resistance heating apparatus, a sheath plate having spaced apertures formed therein, an elongated electrical resistor coil adapted for having an electric current passed therethrough, insulating means securing portions of the turns of the resistor coil to one side of the sheath plate, the resistor coil being located between the apertures and having portions 01' its turns exposed, and reflector means spaced from the sheath plate and the resistor coil at the resistor coil side of the sheath plate, whereby heat from the resistorcoil is transmitted to the plane of the other side of the sheath plate by conduction, convection, radiation, and reflection.

6. In electric resistance heating apparatus, a sheath plate having spaced apertures formed therein, means forming elongated grooves bev tween the apertures at one side of the sheath sheath plate having spaced apertures formed therein, .an elongated electrical resistor adapted for having an electric current passed therethrough, insulating means securing portions of the resistor to one side of the sheath p1ate, the resistor, being located between the apertures and having elongated exposed portions, and reflector means spaced from the sheath plate and the resistor at the resistor side thereof, whereby heat from the resistor is transmitted to the plane of the other side of the sheath plate by conduction, convection, radiation, and reflection,-'the reflector means including a member having a reflecting surface opposite the resistor and the reflector member having an aperture formed therein.

8. In electric resistance heating apparatus, a sheath plate having spaced apertures formed therein, an elongated electrical resistor adapted for having an electric current passed therethrough, insulating means securing portions of the resistor to one side of the sheath plate, the

resistor being located between the apertures and having elongated exposed portions, and reflector means spaced from the sheath plate and the resistor at the resistor side thereof, whereby heat a from the resistor is transmitted to the plane of the other side of the sheath plate by conduction, convection, radiation, and reflection, the reflector means including a member having a conical reflector surface formed therein opposite the resistor.

9. In electric resistance heating apparatus, a sheath plate having spaced apertures formed therein, an elongated electrical resistor adapted convection, radiation, and reflection, the reflector means including a member having a conical reflector surface formed therein opposite the resistor, and the reflector member having an aperture formed therein.

10. In unitary electric resistance heating apparatus, a sheath plate having an aperture formed therein, an electrical resistor arranged about the aperture at one side of the sheath plate, insulating means embedding and securing portions of the resistor adjacent the sheath plate to the one side of the sheath plate, and reflector means spaced from the sheath plate at the side thereof having secured thereon the partially embedded resistor, whereby heat from the resistor is transmitted to a heating plane at the other side of the sheath plate by conduction, convection, radiation, and reflection.

ARLINGTON BENSEL. WILLIAM* A. BRAUN.

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